'undesirability' originates from the negative prefix 'un-' (Old English) plus 'desirability.' 'Desirability' derives from Old French 'desirabilite' and ultimately from Latin 'desiderare,' where the root meant 'to long for' or 'wish for.'

'undesirability' changed from the combination of Old English/Middle English prefix 'un-' + Middle English/Old French-derived 'desirability' (e.g. Middle English 'desirabilite') and eventually became the modern English noun 'undesirability.'

Initially, it meant 'the state of not being desired or wished for,' but over time it has come to cover both that basic sense and the idea of 'the degree or specific feature that makes something undesirable.'